The flag of the United Kingdom, not of England, (called Union Flag or Union Jack) is really a combination of the three crosses of the patron saints that make up the territory of the United Kingdom, England, Scotland, and Northern Ireland.
The red cross on a white background of the center, is that of St. George of England. The white cross on a blue background is the cross of Saint Andrew of Scotland. And the red cross on a white background is the cross of Saint Patrick of Ireland.
